Various machines are known in the prior art for progressively forming blanks by passing them through sequential die stations until they conform to a desired size and shape. Successive draws take an initially flat blank of metal and deform it in such a manner so as to prevent wrinkles and cracks from forming in the blank. This is true even though its shape is changed to one that is intended depending upon the particular application to which the work piece is to be put. The ultimate application may be a medical enclosure for a defibrillator or a pacemaker.
Prior art structures employ tools for each individual draw. In some instances, the case needs to be washed and annealed in order to maintain a sufficient degree of pliability for the next successive draw. The time element can be critical in going from draw to draw. Depending upon the number of draws necessary and the treatment between draws, it can take several weeks to complete a particular work piece.
The specific process typically utilized in the prior art passes parts in what is known as a common pass line. In such a methodology, all the presses are in the same horizontal plane. All the tooling has to be in that horizontal plane, and the work pieces are inserted into the draw tool and extracted from the draw tool from the same surface. Such methodology substantially effects drawing the work piece twice because the metal passes twice over the surfaces that actually effect deformation. Such a process can reduce quality by deforming the work piece to push back out a tool. By doing so, a geometry change can occur.
As was previously discussed, time can be an important factor. In one application of such a methodology, a period of time of 45 minutes between draws can be excessive. There is a natural tendency to allow a quantity of work pieces to build up at one machine before they are passed to the next machine. Similarly, because of break time and shift changes, parts may sit unattended for in excess of 45 minutes.
It is to these dictates and shortcomings of the prior art that the present invention is directed. It includes apparatus and methods for sequentially forming a plurality of thin metallic skin structures which solve problems in the prior art.